The present invention relates to the fabrication of color television picture tubes. In the manufacturing of such color television picture tubes an array of phosphor patterns are deposited upon the interior surface of the glass faceplate via a photoresist exposure process in which a polymerizable binder material is utilized to adhere the inert phosphor compositions to the glass faceplate. The phosphor patterns are laid down via a slurrying process, with repetitive washings which can remove non-adherent material. In order to promote good adherence of the polymerizable phosphor composition containing slurry, it has been the practice to first apply a thin precoat of highly insoluble, high molecular weight polyvinyl alcohol containing aqueous slurry upon the glass faceplate panel. The high molecular weight material is typically utilized in a concentration of about 0.075 weight percent polyvinyl alcohol, in the precoat slurry. To further improve the adherence of the precoat layer to the glass faceplate it has been the practice to include a predetermined amount of colloidal silica, about 0.075 weight percent, which is uniformly dispersed throughout the slurry to promote further adherence of the precoat to the glass faceplate, and to also promote adherence of the later applied polymerizable phosphor arrays.
The complete fabrication process for preparing such color television picture tubes is set forth in greater detail in U.S. Pat. No. 3,712,815 issued Jan. 23, 1973, and owned by the assignee of the present invention. It should be understood that after deposition of the phosphor array layer and an opaque non-reactive material between the phosphor arrays that the polymerized organic constituents are removed from the picture tube prior to final seal of the picture tube during a high temperature lehr operation. In other words all the organic material which has been utilized in production and fabrication of the faceplate panel must now be removed via a decomposition and outgassing process. It is therefore desirable to minimize the required amount of organic material necessary in the fabrication process. The inclusion of the colloidal silica in the precoat slurry has been required to achieve high adherence of the precoat glass faceplate panel, yet its inclusion necessitates careful control of the dispersion and drying process to prevent formation of what are termed precoat stains. Such precoat stains are produced as a result of selective drying and accumulation of the colloidal silica on specific areas of the faceplate panel and constitute a visual defect which can be carried through to the completed picture tube.